In recent years, the projector market has been expanding in conjunction with the proliferation of personal computers. Transmissive and reflective liquid crystal display devices are representative of projectors that optically modulate a light beam from a light source in order to produce a light signal for providing a projected image. This type of liquid crystal display device requires that the liquid crystal displays be illuminated with light polarized in a particular direction. This is achieved by using a polarizing beam splitter in the light path from the light source ahead of the liquid crystal displays.
It is also known to use in such liquid crystal display devices light integrators that include two integrator plates in optical series that each includes a two-dimensional array of lenses in order to increase the uniformity of the intensities, in cross-section, of the light beams that illuminate the liquid crystal displays. For example, bright polarizing illumination optical systems using an integrator and a polarizing beam splitter are disclosed in Japanese Laid-Open Patent Applications H08-304739 and H11-183848. The devices described in these publications provide conversion to a polarized light illumination beam by first increasing the uniformity of the cross-sectional intensity of the illuminating light with an integrator plate and then passing the more uniform light beam through a polarizing beam splitter where images of the light source are formed.
The polarizing beam splitter used is a so-called xe2x80x98comb-typexe2x80x99 that includes a plurality of polarization converter elements, one of each corresponds to a lens of an integrator plate. Each element aligns the polarization direction of the light it transmits with a desired polarization direction without greatly reducing the quantity of light it transmits, thereby providing a bright illuminating beam to a liquid crystal display.
However, in the devices of the Japanese patent applications noted above, because the light beams that are emitted from an integrator plate enter into the comb-type polarization converter elements at non-normal angles, the efficiency of the polarization converter elements is reduced. Additionally, with the comb-type elements, as indicated by the term xe2x80x9ccomb-type,xe2x80x9d adjacent portions where light is directly transmitted and where light is not directly transmitted define a stripe-shaped structure where some of the light intended to be directly transmitted becomes mixed with the light not intended to be directly transmitted. This results in a reduction in the total amount of light transmitted.
The precision processing required of the fine stripe-shaped polarization converter elements is costly and is subject to manufacturing problems. Additionally, although problems of reduced total light output can be reduced by the use of a decentering system with an integrator plate, this introduces problems of cost and precision processing related to manufacturing a polarizing illumination optical system with such a decentering system.
The present invention relates to a polarizing illumination optical system and a projection display device using same that provides a uniform and bright illumination beam, is of simple construction, and can be manufactured while reducing the costs associated with precision processing during manufacture. More specifically, the present invention relates to an illumination optical system that uses polarized light to illuminate a liquid crystal display panel, or a similar display for displaying images, and a projection display device that magnifies and projects an image from such a display onto a screen. In particular, the present invention relates to a polarizing illumination optical system for a projection display device that avoids light shielding problems associated with prior art polarizing illuminating optical systems that reduce the amount of illuminating light.